Recently, hybrid vehicles and electric vehicles using a motor as a driving source are widely used. In order to control motor output properly, it is important to measure a current flowing through the motor. As a method of measuring such a current, for example, there is a method in which, according to a current flowing through a busbar that connects a DC brushless motor to an inverter, a magnetic field generated around the busbar is magnetically concentrated by a core made of a magnetic body and is detected by a magnetic detection element such as a Hall element, and the current flowing through the busbar is calculated based on the detected magnetic field, for example, as disclosed in JP 2010-203910A (Reference 1) and JP 2009-42003A (Reference 2).
The current sensor disclosed in Reference 1 includes an annular magnetic core with a gap portion provided at a part thereof, and a metal plate provided on the magnetic core and having a shielding effect. The magnetic core and the metal plate are formed by insert molding with a mold resin.
The current sensor disclosed in Reference 2 includes a ring-shaped magnetic concentration core having a gap. The magnetic concentration core is formed by insert molding in a resin case in such a way that the periphery of the gap is exposed to an internal space connecting to an opening.
In the techniques disclosed in References 1 and 2, the core (the magnetic core and the magnetic concentration core are collectively referred to as the “core”) is fixed to the case or the like by insert molding. Therefore, a compressive strain is applied to the core according to the compressive stress of the resin, and the hysteresis increases. Since the hysteresis characteristic of the current sensor deteriorates, the current cannot be detected accurately.